Electric fields and substrates dramatically accelerate spin relaxation in graphene
Electric fields and substrates dramatically accelerate spin relaxation in graphene
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DOI：
10.1103/physrevb.105.115122
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发表时间：
2022-03-16
影响因子：
3.7
通讯作者：
Sundararaman, Ravishankar
中科院分区：
文献类型：
--
作者：
Habib, Adela;Xu, Junqing;Sundararaman, Ravishankar
理论上，石墨烯中的电子比大多数材料保持自旋状态的时间要长得多，这使得石墨烯成为自旋电子学和量子信息技术的一个有前途的平台。在这里，我们使用第一性原理密度矩阵（FPDM）动力学模拟表明，电场和衬底的相互作用通过声子散射强烈增强了自旋弛豫。因此，室温下的弛豫时间从独立石墨烯中的微秒减少到六方氮化硼（hBN）衬底上的石墨烯中的纳秒，这是实验中通常测量的数量级。此外，hBN的逆对称性破缺在电子和空穴自旋寿命方面引入了比传统的D? yakonov-Perel？（DP）自旋弛豫模型。平面内自旋松弛与传统DP模型的偏差更大，导致面外与面内寿命比远远大于1/2，最大值接近Dirac点。这些FPDM结果，独立于对称性特定假设或材料相关参数，也验证了DP模型最近的修改，以解释这些偏差。总的来说，我们的研究结果表明，在衬底存在的情况下，自旋声子弛豫在石墨烯中可能比通常假设的更重要，这需要考虑室温下石墨烯基自旋技术。
Electrons in graphene are theoretically expected to retain spin states much longer than most materials, making graphene a promising platform for spintronics and quantum information technologies. Here, we use first-principles density-matrix (FPDM) dynamics simulations to show that interaction with electric fields and substrates strongly enhances spin relaxation through scattering with phonons. Consequently, the relaxation time at room temperature reduces from microseconds in free-standing graphene to nanoseconds in graphene on the hexagonal boron nitride (hBN) substrate, which is the order of magnitude typically measured in experiments. Further, inversion symmetry breaking by hBN introduces a stronger asymmetry in electron and hole spin lifetimes than predicted by the conventional D???yakonov-Perel??? (DP) model for spin relaxation. Deviations from the conventional DP model are stronger for in-plane spin relaxation, resulting in out-of-plane to in-plane lifetime ratios much greater than 1/2 with a maximum close to the Dirac point. These FPDM results, independent of symmetry-specific assumptions or material-dependent parameters, also validate recent modifications of the DP model to explain such deviations. Overall, our results indicate that spin-phonon relaxation in the presence of substrates may be more important in graphene than typically assumed, requiring consideration for graphenebased spin technologies at room temperature.